Please explain the following four lines from the first sonnet of Sir Philip Sydney's Astrophel And Stella.
"I sought fit words to paint the blackest face of woe,
Studying inventions fine, her wits to entertain,
Oft turning others' leaves, to see if thence would flow
Some fresh and fruitful showers upon my sun-burn'd brain."
As the first quatrain, the second quatrain of Sir Philip Sidney's "Astrophel and Stella" is written in iambic hexameter rhymed ABAB. It describes the process of the poet trying to compose the poem. First, the poet says that he is trying to find words to describe his unhappiness at unrequited love. He studies "invention", the first canon of rhetoric that forms a system for discovering arguments or ideas to support a position. This probably refers to reading the examples of other authors and consulting Cicero and Horace, and thus turning the leaves or pages of their books. He then uses the metaphor of their wisdom fertilizing his imagination as the rain makes parched earth moist enough for plants to grow.